1. Field of the Invention
The present invention relates to liquid copolymers of mercaptan-terminated polymers such as polysulfides and epoxy-terminated polymers such as epoxy resins which can be stored as prepolymers before final curing to form solid products.
2. Description of the Prior Art
The production of resins by coreacting polysulfides with polyepoxides in the presence of a catalyst is well known. The reaction between the mercaptan groups of the polysulfide and the oxirane groups of the polyepoxide proceeds easily and is the basis of U.S. Pat. No. 2,789,958, which describes the production of resinous reaction products of polyepoxides and polysulfides and methods of making them. All but one of the examples given in the U.S. Pat. No. 2,789,958 describe the reaction between liquid polysulfides and so-called polyepoxide curing agents in the presence of amine catalysts. The cured products were hard, tough, sometimes rubbery materials. In the other example, the polysulfide polymer was reacted with the polyepoxide curing agents, in the absence of amine catalyst, at 70.degree. C. for six hours and at 25.degree. C. for two days. The product was a tough rubbery polymer.
The invention described in the U.S. Pat. No. 2,789,958 formed the basis for the use of liquid polysulfide polymers as flexibilizers for polyepoxy resins. In these systems the liquid polysulfide polymer is mechanically mixed into the polyepoxide resin together with a catalyst, usually a tertiary amine. The resulting products are tough, impact resistant solids, which if necessary adhere to a wide range of substrates.
The products of such processes have been used in the production of adhesives, coatings, electronic encapsulation systems and moldings.
No. GB-A-787 022 describes self-hardening resins made by mixing liquid or semisolid epoxide resins and liquid aliphatic saturated polythiopolymercaptans. These resins generally cure to a hard rubbery state within 24 hours or in a few cases 48 hours.
Despite their undoubted success as tough, chemically resistant coatings and adhesives, current LP/epoxy systems suffer from the limitations of a mercaptan odour emanating from the polysulfide component, which persists until the system begins to cure.
U.S. Pat. No. 3,101,326 discloses the reaction of a polysulfide with styrene oxide to reduce or eliminate the mercaptan odor. The product can be used to flexibilize epoxy resins.